Traction battery assembly

ABSTRACT

A traction battery assembly includes adjacent battery cells supported by a tray and a busbar electrically connecting the adjacent battery cells. The busbar includes a longitudinal midpoint and a pair of bowed sections joined at the midpoint. Each of the bowed sections has an actuate portion in contact with a terminal on one of the cells. The bowed sections provide increased contact with the cells when the cells have different elevations with respect to the tray. A busbar module is also disclosed. The busbar module comprises a housing and a busbar supported within the housing.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a division of U.S. application Ser. No. 14/134,290filed Dec. 19, 2013, now U.S. Pat. No. 9,653,720, issued May 16, 2017,the disclosure of which is hereby incorporated in its entirety byreference herein.

TECHNICAL FIELD

This disclosure relates to busbars for vehicle traction batteryassemblies.

BACKGROUND

Vehicles such as battery-electric vehicles (BEVs), plug-in hybridelectric vehicles (PHEVs) or hybrid-electric vehicles (HEVs) contain abattery pack with a traction battery to act as an energy source for thevehicle. The battery pack may include components and systems to interactwith the battery and assist in managing vehicle performance andoperations. The battery pack may include one or more arrays of batterycells with the cell terminals interconnected electrically with busbars.

SUMMARY

A busbar with a pair of curved sections is provided for increasing thecontact area between the cell terminals and the curved sections when thecell terminals are at different heights with respect to each other.

In one embodiment, a traction battery assembly comprises adjacent cellsincluding a planar terminal. One planar terminal on each cell iselectrically connected by a busbar. The busbar has a longitudinalmidpoint and defines a pair of bowed sections joined at the midpoint. Anarcuate portion along each of the bowed sections is in contact with oneof the terminals when the terminals are at different elevations relativeto a battery tray to provide increased contact between the busbar andterminals.

In another embodiment, a traction battery assembly comprises a tray andadjacent cells supported by the tray. A housing is disposed on the cellsopposite the tray and spans the adjacent cells. The housing has a pairof opposing sidewalls cooperating to define an enclosure. A busbar isreceived within the enclosure. The busbar has a longitudinal midpointand a pair of bowed sections joined at the midpoint. Each of the bowedsections is in contact with one of the terminals when the terminals areat different elevations relative to the tray to provide increasedcontact between the busbar and terminals.

In yet another embodiment, a traction battery assembly comprisesadjacent cells supported by a tray. Each of the cells has a terminal. Abusbar electrically connects the cells. The busbar has a longitudinalmidpoint and defines a pair of rockers connected at the midpoint. Eachof the rockers has a curved portion in contact with one of theterminals. The curved portions are configured to rock along theterminals to provide increased contact between the busbar and terminalswhen the busbar has an angled orientation caused by a height differencebetween the terminals.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a prior art busbar.

FIG. 2 is a perspective view of a traction battery assembly.

FIGS. 3A and 3B are side views of prior art busbar and terminalarrangements.

FIG. 4 is a perspective view of a busbar.

FIGS. 5A and 5B are side views of busbar and terminal arrangements.

FIG. 6 is a side view of another busbar and terminal arrangement.

FIG. 7 is a perspective view of a pin and slot busbar module.

FIG. 8 is a perspective view of a curled edge busbar module.

FIG. 9 is a perspective view of another busbar.

DETAILED DESCRIPTION

Embodiments of the present disclosure are described herein. It is to beunderstood, however, that the disclosed embodiments are merely examplesand other embodiments can take various and alternative forms. Thefigures are not necessarily to scale; some features could be exaggeratedor minimized to show details of particular components. Therefore,specific structural and functional details disclosed herein are not tobe interpreted as limiting, but merely as a representative basis forteaching one skilled in the art to variously employ the presentinvention. As those of ordinary skill in the art will understand,various features illustrated and described with reference to any one ofthe figures can be combined with features illustrated in one or moreother figures to produce embodiments that are not explicitly illustratedor described. The combinations of features illustrated providerepresentative embodiments for typical applications. Variouscombinations and modifications of the features consistent with theteachings of this disclosure, however, could be desired for particularapplications or implementations.

Referring to FIG. 1, a prior art busbar is shown. The busbar 1 has abody 3 with a first terminal connector 5 and a second terminal connecter7 at opposing ends. The busbar 1 has two semicircular cut-outs 9 sizedand shaped to connect to a corresponding circular battery terminal.

Referring to FIG. 2, electric vehicles may include an energy systemhaving a traction battery assembly 10 with components such as one ormore battery cell arrays 12, a battery electrical control module (BECM),and a direct current to direct current (DC/DC) converter unit. Thebattery cell arrays 12 provide energy to operate the vehicle and itssystems. The battery arrays 12 are in electrical communication with theBECM, DC/DC converter unit and other vehicle components. The BECMreceives input signals from various systems, processes informationincluded in the input signals and generates appropriate control signalsin response thereto. These control signals activate and/or deactivatethe various components. The DC/DC converter unit converts high voltagefrom the battery cell arrays into low voltage for use by the componentsand other systems.

The battery assembly 10 includes a tray 20 for supporting the batteryarrays 12. Each battery array 12 is received on the tray 20 and includesa plurality of battery cells 18 connected in series and/or parallel. Thebattery cells 18, such as a prismatic cell, convert stored chemicalenergy to electrical energy. The cells 18 include a housing, a positiveelectrode (cathode) and a negative electrode (anode). An electrolyteallows ions to move between the anode and cathode during discharge, andthen return during recharge. Terminals allow current to flow out of thecell for use by the vehicle. When positioned in an array with multiplebattery cells, the terminals of each battery cell are aligned withopposing terminals (positive and negative) adjacent to one another tofacilitate a series connection between the multiple battery cells.Busbars may be used to assist in completing the series connectionbetween adjacent battery cells or groups of battery cells proximate toone another. Different battery pack configurations may be available toaddress individual vehicle variables including packaging constraints andpower requirements.

Battery cell dimensions may vary within a given tolerance due tomanufacturing imperfections, thus adjacent cells may be of slightlydifferent dimension. The positing of the cells 18 in the array 12 alsomay vary within a given tolerance due to manufacturing imperfections.These imperfections make it common for adjacent cells 18 to haveslightly different heights with respect to each other.

A height differential between adjacent cells can cause connectionsproblems between the cell terminals and the busbar because busbars aretypically made of rigid, metallic materials. Two possible problems thatcan occur are illustrated in prior art FIGS. 3A and 3B. In FIG. 3A, astraight busbar 11 is connected to two adjacent cell terminals 13 ofdifferent height. The height difference between the terminals causes thebusbar 11 to have an angled orientation with respect to the top of theterminals. The angled orientation of the busbar 11 provides a smallbusbar-terminal interface 15 and a gap 17 between the busbar 11 and theterminals 13. The contact region may be too small to provide for asatisfactory weld and may be in a location that is difficult to locatedduring a welding operation such as the very edge of the terminal.Therefore the weld 19 must extend past the busbar-terminal interface 15into the gap 17. Welding at the gap 17 requires additional weldingmaterials and time. Welding at the gap may also preclude some methods ofwelding which cannot tolerate a large gap.

In FIG. 3B, a straight busbar 21 is connected between two adjacent cellterminals 23 of different height. The busbar 21 is pushed flush againsteach terminal 23. This eliminates the gaps and increases thebusbar-terminal interface, but also creates higher stress regions on thebusbar 21. Pushing the busbar 21 flush also bends the busbar causingdeformation at area 25 proximate the midpoint of the busbar 21. Thisdeformation 25 cold works the busbar 21 and can affect the electricalproperties of the busbar 21. The elasticity of the busbar causesincreased stress at the terminal-busbar connection 27. This stress overtime may fatigue the weld 29 leading to connection issues. A strongerweld may be used to combat the fatigue, but this may increase productioncost. The process of pushing the busbar flush against each terminal mayalso have undesirable effects on the cells in the array if the pushingforce is transferred to the array. The process of pushing may also addcost to the array connection process and require additional clearanceproximate to the cell terminals to push and hold the busbar in placeduring the welding operation.

Referring to FIG. 4, a busbar 22 according to the present disclosure isshown. The busbar 22 is a single strip of metal such as copper oraluminum. The busbar 22 has a longitudinal midpoint 24 and twolongitudinal endpoints 26 distal to the midpoint 24. The busbar 22includes a pair of bowed sections 28 defined between the midpoint 24 anda corresponding end point 26. The bowed sections 28 are symmetricalabout the midpoint 24. However, the bowed sections 28 may beasymmetrical in certain applications. The bowed sections 28 have acrescent shaped curvature in the longitudinal direction 30 and are flatin the transverse direction 32.

Referring to FIGS. 5A and 5B, an elevation view looking at the long sideof the battery array 12 is shown. The battery array 12 has a tray 20supporting adjacent cells 18. A first cell terminal 36 is extends fromone of the cells and a second cell terminal 38 extends from the othercell. The terminals 36, 38 are planar terminals having a generallyrectangular shape and a flat top. The first and second terminals 36, 38are electrically connected by the busbar 22. The busbar 22 has amidpoint 24 and two endpoints 26. The midpoint 24 and end points 26define a first bowed section 40 and a second bowed section 42. The firstbowed section 40 connects to a first cell terminal 36 at a first arcuateportion 44 and the second bowed section 42 connects to the second cellterminal 38 at a second arcuate portion 46.

Referring to FIG. 5A, the distal ends 48 of the first and secondterminals 36, 38 have the same elevation with respect to the tray 20.The busbar 22 is disposed on the distal end 48 of the terminals 36, 38at the first and second arcuate portions 44, 46. The busbar 22 isgenerally horizontal with the first and second bowed sections 40, 42having the same elevation with respect to the tray 20. Thebusbar-terminal interface 50 a, 50 b on each of the arcuate portions issymmetrical about the midpoint 24 and is centered on the terminals 36,38. The bowed sections 40, 42 have a weldable range 52 a, 52 b along amajority of the bowed section beginning at a corresponding endpoint 26and extending towards the midpoint 24.

Referring to FIG. 5B, the distal ends 48 of first and second terminals36, 38 have a different elevation with respect to the tray 20. The firstterminal 36, for example, is 0.70 mm higher than the second terminal 38.The busbar 22 is disposed on the distal end 48 of the terminals 36, 38with the first bowed section 40 being higher than the second bowedsection 42 with respect to the tray 20. The elevation differentialbetween the terminals 36, 38 causes the busbar 22 to pivot about themidpoint 24 and has an angled orientation with respect to the tray. Thecurvature of the first and second bowed sections 40, 42 cooperate witheach other to provide an increased busbar-terminal interface 50 a, 50 band weldable range 52 a, 52 b when the busbar 22 is in the angledorientation.

Comparing FIGS. 5A and 5B, the busbar-terminal interface 50 a along thefirst bowed section 40 in FIG. 5B has shifted towards the midpoint 24 asthe bowed section 40 rocked on the terminal 36 due to the elevationdifference between the terminals. The rocking of the first bowed section40 does not affect the size of the busbar-terminal interface 50 a due tothe curvature of the bowed section 40. The rocking increases the size ofthe weldable range 52 a and shifts the weldable range 52 a towards themidpoint 24.

The busbar-terminal interface 50 b along the second bowed section 42 inFIG. 5B has shifted away from the midpoint 24 as the bowed section 42rocked on the terminal 38 due to the elevation difference between theterminals. The rocking of the second bowed section 42 does not affectthe size of the busbar-terminal interface 50 b due to the curvature ofthe bowed section 40. The rocking decreases the size of the weldablerange 52 b and shifts the weldable range 52 b towards the midpoint 24.Even though the weldable range 52 b has decreased in size in FIG. 5B, itis still large enough to provide a satisfactory connection. While FIGS.5A and 5B only illustrate two cells, a person skilled in the art willunderstand that more than two cells can be interconnected by busbars toform an array.

Referring to FIGS. 6 and 7, a busbar module 54 is shown. The busbarmodule 54 comprises a housing 56 and a busbar 22 supported by thehousing 56. The busbar housing 56 protects the busbar 22 and serves as alocating device during installation of the busbar 22 onto the batteryarray 12. The housing 56 has a first sidewall 58 and a second sidewall60 connected together by a pair of opposing end walls 62 to form arectangular box. The first sidewall 58 has a first slot 64 arrangedperpendicular to a longitudinal axis 68 of the first sidewall 58. Thesecond sidewall 60 has a similarly arranged second slot 66. The secondsidewall 60 has a notch 70 opening into the slot 66. The slots 64, 66are centered at the midpoint of their corresponding sidewalls 58, 60.The housing 56 has a generally open bottom 72 with two partial bottomwalls 80. The bottom walls 80 extend from a corresponding end wall 62partially along the sidewalls 58, 60. The sidewalls 58, 60 and bottomwalls 80 define the open bottom 72. The housing 56 has a generally opentop 76, which may be covered at a later point to restrict access to theterminals and bussing. The top 76 has two ledges 84. Each of the ledges84 protrudes into the housing 56 from the first sidewall 58 and acorresponding end wall 62. The ledges 84 have an interior portion 86.The interior portion 86 has a straight portion 88 parallel to the endwalls 62 and a tampered portion 90 extending from the straight portion88 and terminating at a corresponding end wall 62. The ledges 84 do notfully span the end wall 62 providing a full open top along the secondsidewall 60. While the busbar module 54 depicted includes a top and abottom, the present disclosure contemplates a busbar module 54 having acompletely open top and bottom. Alternatively, the busbar module 54 mayonly have a top and not a bottom, or vice versa.

The housing 56 defines an enclosure 92 for receiving the busbar 22therein. The busbar 22 has a first projection 94 extending outwardlyfrom a first side 96 of the busbar 22 and a second projection 98extending outwardly from a second side 100 of the busbar 22. The firstside 96 of the busbar 22 is inserted into the enclosure 92 first. Thefirst side 96 is inserted through the open top 76 at the largest portionof the opening proximate the second sidewall 60. The first projection 94is received within the first slot 64. The second projection 98 isreceived though the notch 70 and into the second slot 66. The slots 64,66 and the projections 94, 98 cooperate to allow the busbar 22 to rotateabout the projections 94, 98 and to move perpendicular but not parallelto the longitudinal axis 68 of the sidewalls 58, 60. The ledges 84 andthe bottoms walls 80 cooperate to prevent the busbar 22 from rotatingbeyond a desired range.

Referring to FIG. 6, the busbar module 54 sits on and spans across theadjacent cells 18. The terminals 36, 38 are received into the housing 56through the hole 82. The busbar 22 self-adjusts for height along theslots 64, 66 to correctly position on the terminals 36, 38. The busbar22 self-adjusts for rotation by pivoting in the slots about theprojections 94, 98 and allowing the bowed sections 40, 42 to rock alongthe terminals and correctly seat. After the busbar module 54 has locatedthe busbar 22 into position, additional tooling can be used to weld thebusbar 22 to the terminals 36, 38. Additional tooling could also be usedto vibrate the busbar module 54 to ensure that the busbar 22 is properlyseated on the terminals 36, 38.

Referring to FIG. 8, an alternative busbar module 254 is shown. Thebusbar module 254 comprises a housing 256 and a busbar 222 supported bythe housing 256. The housing 256 has a first sidewall 296 and a secondsidewall 200 connected together by a pair of opposing end walls 262 toform a rectangular box and define an enclosure 206. The housing 256 hasa generally open bottom 272 with two partial bottom walls 280. Thebottom walls 280 extend from a corresponding end wall 262 partiallyalong the sidewalls 200, 296. The sidewalls 200, 296 and bottom walls280 define an opening. The housing 256 has a generally open top 202. Thetop has two ledges 284. Each of the ledges 284 protrudes into thehousing 256 from the first sidewall 296 and a corresponding end wall262. The ledges 284 have an interior side 286. The interior side 286 hasa straight portion 288 parallel to the end walls 262 and a taperedportion 290 extending from the straight portion and terminating at acorresponding end wall 262. The ledges 284 do not fully span the endwalls 262 providing a full opening along the second sidewall 200.

The busbar 222 has a midpoint and a pair of endpoints 226. Each of theendpoints 226 has a curled edge 204. The busbar 222 is received with theenclosure 206 through the open top 202. The curled edges 204 engage withthe end walls 262 to align and position the busbar 222 within thehousing 256. The curled edges 204 and the end wall 262 cooperate toallow motion perpendicular to the sidewalls 296, 200 but notlongitudinally. The ledges 284 and the bottoms walls 280 cooperate toprevent the busbar 222 from rotating beyond a desired range.

FIG. 9 illustrates a busbar 322 of an alternative embodiment. UnlikeFIG. 6, the first and second projections 394, 398 in this embodiment areintegrally formed by deforming a portion of the main body 300 of thebusbar 322. The first projection 394 is formed by cutting the main body300 at surface 304. The first projection 394 is then bent away from themain body 300 to form a first projection 394 that extends outwardly fromthe midpoint 324. The second projection 398 is formed in the samemanner. This embodiment provides a smallest cross-sectional area alongline 302. Line 302 also has work hardening stress resulting from thebending operation. The smaller cross-sectional area and work hardeningproduce a high resistance point along line 302 which can be tuned toserve as a fuse. This may eliminate the need to provide additional fusesand may also be helpful in satisfying the abuse test conditions forshipping lithium ion batteries.

While exemplary embodiments are described above, it is not intended thatthese embodiments describe all possible forms encompassed by the claims.The words used in the specification are words of description rather thanlimitation, and it is understood that various changes can be madewithout departing from the spirit and scope of the disclosure. Aspreviously described, the features of various embodiments can becombined to form further embodiments of the invention that may not beexplicitly described or illustrated. While various embodiments couldhave been described as providing advantages or being preferred overother embodiments or prior art implementations with respect to one ormore desired characteristics, those of ordinary skill in the artrecognize that one or more features or characteristics can becompromised to achieve desired overall system attributes, which dependon the specific application and implementation. These attributes caninclude, but are not limited to cost, strength, durability, life cyclecost, marketability, appearance, packaging, size, serviceability,weight, manufacturability, ease of assembly, etc. As such, embodimentsdescribed as less desirable than other embodiments or prior artimplementations with respect to one or more characteristics are notoutside the scope of the disclosure and can be desirable for particularapplications.

What is claimed is:
 1. A traction battery assembly comprising: an arrayof cells including an adjacent pair of cells that each have a planarterminal; and a plurality of busbar modules each having a housing and abusbar disposed in the housing, a first of the busbar modules includinga first housing having a bottom disposed on the pair of cells and endwalls extending upward from the bottom, and including a first busbarhaving a longitudinal midpoint and defining a pair of bowed sectionsjoined at the midpoint, wherein an arcuate portion along each of thebowed sections is in contact with one of the terminals.
 2. The assemblyof claim 1 wherein each of the bowed sections has a curled edgeconfigured to engage with one of the end walls.
 3. The assembly of claim1 wherein the pair of bowed sections are symmetrically arranged aboutthe midpoint.
 4. The assembly of claim 1 wherein the bottom includes apair of partial walls each connected to one of the end walls, the pairof partial walls being spaced apart to define an opening in the bottomthat receives the terminals therethrough.
 5. The assembly of claim 1wherein the first housing further includes a pair of opposing sidewallsextending between the end walls.
 6. The assembly of claim 5 wherein thefirst housing further includes a pair of ledges each extending from oneof the end walls and connected to only one of the sidewalls, the ledges,sidewalls, and end walls cooperating to define an open top of the firsthousing.
 7. The assembly of claim 6 wherein the ledges are connected toa same one of the sidewalls.
 8. A traction battery assembly comprising:a tray; a pair of adjacent cells supported by the tray and includingadjacent terminals with one terminal being part of each cell; a housingpositioned on the cells opposite the tray and spanning the cells,wherein the housing has a pair of opposing sidewalls cooperating todefine an enclosure that receives the terminals, and each of thesidewalls defines an aperture; and a busbar received within theenclosure and extending in a same direction as the sidewalls, the busbarhaving a longitudinal midpoint and a pair of bowed sections joined atthe midpoint, wherein each of the bowed sections is in contact with oneof the terminals when the terminals are at different elevations relativeto the tray to provide increased contact between the busbar andterminals, and the busbar further has a pair of projections eachextending substantially perpendicular from the longitudinal midpoint andreceived in one of the apertures.
 9. The traction battery assembly ofclaim 8 wherein each of the apertures is a slot arranged perpendicularto a longitudinal axis of a corresponding one of the sidewalls and isconfigured to allow the busbar to move perpendicular but not parallel tothe longitudinal axis of the corresponding sidewall.
 10. The assembly ofclaim 8 wherein a cross-sectional area of the midpoint is less than across-sectional area of end portions of the bowed sections such that themidpoint has a resistance greater than a resistance of the end portions.11. The traction battery assembly of claim 8 wherein the midpoint andbowed sections are configured such that an electrical resistance of themidpoint is greater than a resistance of the bowed sections.
 12. Atraction battery comprising: adjacent cells each including a terminal; abusbar module spanning the cells and including opposing sidewallsdefining slots and an enclosure that receives the terminals; and abusbar having a longitudinal midpoint and defining a pair of rockersconnected at the midpoint and projections each extending perpendicularlyfrom the midpoint and into one of the slots, each of the rockers havinga curved portion in contact with one of the terminals.
 13. The tractionbattery of claim 12 wherein the pair of rockers are arrangedsymmetrically about the midpoint.
 14. The traction battery of claim 12wherein the adjacent cells are prismatic cells that include terminalsides from which the terminals extend, and each of the sidewalls aredisposed against each of the terminal sides.
 15. The traction battery ofclaim 12 further comprising: second adjacent cells each including aterminal; a second busbar module spanning the second adjacent cells andincluding opposing sidewalls defining slots and an enclosure thatreceives the terminals of the second adjacent cells; and a busbar of thesecond busbar module having a longitudinal midpoint and defining a pairof rockers connected at the midpoint and projections each extendingperpendicularly from the midpoint and into one of the slots of thesecond busbar module, each of the rockers having a curved portion incontact with one of the terminals of the second adjacent cells.